System and method for providing quality of service in ieee 802.11 systems

ABSTRACT

A method for providing quality of services of at least one mobile terminal in a wireless network, such as a 802.11 wireless network, wherein a service proxy functionality within an access point of the network or another entity provide quality of service operations to the at least one mobile terminal.

FIELD OF THE INVENTION

The present invention relates to wireless LAN networks, and moreparticularly, to methods and systems for providing quality of servicewithin IEEE 802.11 systems.

BACKGROUND OF THE INVENTION

The IEEE 802.11 wireless local area network protocol enables wirelesscommunications between access points and mobile terminals within a cell.IEEE 802.11 provides two methods for accessing the access points by themobile terminal. The distributed coordination function (DCF) enables anumber of units to simultaneously contend for access to the network. Thepoint coordination function (PCF) allows an access point to controlaccess to the network. While existing access points can distributebandwidth between mobile terminals within a cell using the pointcoordination function, currently most 802.11 products do not support thepolling mechanism that is used in the point coordination function. Thisleaves a system that may only be used to control downlink traffic andhas very restricted possibilities with respect to QoS.

The IEEE 802.11 standard presently provides no explicit support forquality of service (QoS). A new standard is currently being worked onthat would provide QoS support. However, this update is far from beingimplemented and support for QoS will not exist for a long time. Thus,there is a need for a system that will support systems having no QoSabilities and for systems that may partially support QoS and forproviding some type of differentiated quality of service support withinthe existing 802.11 infrastructure for devices that do not support thepolling mechanism of the point coordination function.

Apart from the IEEE 802.11 Wireless LAN protocol used by the end user ofthe wireless terminal, the IP, the UDP, the RTP (Real-Time TransportProtocol) and the TCP protocol are well known protocols.

SUMMARY

The present invention overcomes the foregoing and other problems with amethod for providing quality of service in an 802.11 wireless networkwherein data received from at least one mobile terminal is processed atan access point or intermediate note using a quality of service proxyfunctionality within the access point or note. The at least one mobileterminal is then provided with a quality of service operation from theaccess point.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention thattogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 illustrates an 802.11 wireless local area network;

FIG. 2 illustrates the operation of the point coordination function;

FIG. 3 illustrates a first embodiment for providing quality of servicewithin an 802.11 WLAN;

FIG. 4 illustrates a further embodiment for providing quality of servicewithin an 802.11 WLAN;

FIG. 5 illustrates yet a further embodiment for providing quality ofservice in an 802.11 WLAN;

FIG. 6 illustrates yet another embodiment for providing quality ofservice in an 802.11 WLAN;

FIG. 7 illustrates a duration/ID field within a frame transmitted froman access point to various mobile terminals;

FIG. 8 illustrates a NAV transmission to multiple STAs;

FIG. 9 illustrates a use of an extended network allocation vector toachieve quality of service within an 802.11 WLAN;

FIG. 10 illustrates one protocol stack of a mobile terminal, AP and peerend user;

FIG. 11 illustrates the IP version 4 protocol format;

FIG. 12 illustrates the IP version 6 protocol format; and

FIG. 13 illustrates the TCP protocol format.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Referring now to the drawings, and more particularly to FIG. 1, there isillustrated an example of a network environment that uses the IEEE802.11 wireless local area network standard. A wireless LAN system 10typically consists of a number of cells 15 each having at least oneaccess point (AP) 20 within each cell 15. Mobile terminals (MT) 25 canassociate with a particular access point 20 and obtain access to theservices provided by the access point 20 connecting to a wired network(not shown). The access points 20 and mobile terminals 25 are sometimesreferred to as stations (STAs). In the following, the term “station” or“STA” is used when referring to both access points and mobile terminalsrather than when each of these are referred to individually.

As mentioned previously, the IEEE 802.11 standard provides two methodsfor accessing the wireless medium, namely, the distributed coordinationfunction (DCF) and the point coordination function (PCF). Thedistributed coordination function is a carrier sense multiple accesswith collision avoidance scheme were all STAs simultaneously contend foraccess to the wireless medium. The STAs listen to the wireless mediumfor a specified amount of time and when it is not busy, an STA beginstransmitting. When collisions occur, a back off mechanism is used toreduce the risk of further collisions. There is in principle no way topredict when a transmission of a certain frame will occur or how muchbandwidth a certain STA will obtain since access to the wireless mediumis dependent on the amount of contention from other STAs in a cell. Itis also not possible to differentiate between STAs since all STAscontend using the same rules irrespective of the type or amount of datafor transmission.

The point coordination function enables an access point 20 to issue acontention free period (CFP) providing the access point 20 control overthe wireless medium. This is illustrated in FIG. 2 wherein a beacon 30transmitted by the access point 20, establishes the contention freeperiod 35 within a particular cell. The contention free period 35 endsupon expiration of a CFP maximum duration period or upon transmission ofa CF-end frame 40 by the access point 20. The contention period 45 isthen in effect wherein the distributed coordination function is used forcommunications until a next beacon 50 is transmitted by an access point20. During the contention free period 35 the access point 20 cantransmit downlink (AP to MT) but the mobile terminals 25 are not allowedto transmit uplink (MT to AP) traffic unless they are polled by theaccess point 20. Thus, using the point coordination function, the accesspoint 20 has control over both the uplink and downlink scheduling.

Since there is no support in IEEE 802.11 for explicit distribution ofbandwidth between mobile terminals 25 in a cell, there is a need to usesome type quality of service proxy 26 (FIG. 1) to act as an intermediatebetween peers that act in quality of service functions. The quality ofservice proxy 26 may be situated in the access point 20, in anintermediate note such as a router. This solution may cause the mobileterminals 25 to experience different bandwidth, delay, packet error rateetc, but the 802.11 layers within the mobile terminal will not be awareof any quality of service differentiation.

Several possible implementations of a proxy are available. With respectto the following discussions, references will be made between preferredusers and regular users with respect to corresponding mobile terminals25. A preferred user, for example, has a more expensive subscriptionwith a WLAN provider than a regular user and will thus receive preferredtreatment within a cell 15. A distinction may also be made betweendifferent types of categories of data, e.g., high priority and lowpriority, but for purposes of the following discussion, reference willonly be made to the user. The access point 20 can use the MAC address ofthe mobile terminals 25 to distinguish between users and/or IEEE802.1Q-tags to distinguish between traffic categories.

Referring now to FIG. 3, there is illustrated a first embodiment when aproxy 26 is implemented within the access point 20. Upon reception of aframe 60 from a regular mobile terminal 25 during a contention period,the access point 20 discards the frame at 65 without transmitting anacknowledgment message to the regular mobile terminal 25 user. When themobile terminal 25 does not receive an acknowledgment for transmissionof the frame, the mobile terminal 25 will increase its contention windowat 70 and retransmit the frame from the mobile terminal 25 to the accesspoint 20 at 75. The larger contention window implies a longer back offtime. The back off time determines the time during which the wirelessmedium has to be idle before an STA is allowed to transmit. Within acell 15 having a lot of contention, this will cause the total contentionto decrease, and mobile terminals 25 that have not increased theircontention window, including all preferred mobile terminals, will havean advantage in accessing the wireless medium.

Referring now to FIG. 4, there is illustrated an alternative embodimentof an implementation of a proxy 26 wherein upon receipt of a frame 80 atthe access point 20 from a regular mobile terminal 25 during thecontention period, the access point 20 acknowledges at 85 the receivedframe as normal to the mobile terminal 25 but discards the frame at 90and does not forward the frame to a wired network connected to theaccess point. This acts to decrease the pace at which higher layers ofthe protocol transmit the data. This decreases the pace at which data istransmitted by a TCP sender. This also reduces the amount of datatransmitted onto the wireless medium by the regular mobile terminal andbecause of that the other mobile terminals, including the preferredmobile terminals, will experience less contention.

Referring now to FIG. 5, there is illustrated yet a further embodimentfor implementation of a proxy, wherein upon reception of a frame 95 froma regular mobile terminal 25 during a contention period, the accesspoint 20 forwards the received frame at 100 to a wired local areanetwork 105 but prevents transmission of an acknowledgment back to theregular mobile terminal sender 25. The response will be essentially thesame as that described with respect to FIG. 3, wherein the mobileterminal 25 will increase its contention window at 110 and retransmitthe frame to the access point 20 at 115. The difference between this andthe example of FIG. 3 will be noticeable on the higher layers, forexample, on the RTT estimates of the TCP layers.

Each time an access point 20 begins a contention free period 35 asdescribed above with respect to FIG. 2, all mobile terminals 25 within acell set their network allocation vector (NAV) to protect the wirelessmedium during the contention free period. As described above, thecontention free period ends when the CFP maximum duration expires orwhen the access point 20 transmits a CF-End frame to the broadcastaddress. The mobile terminals 25 will, upon reception of a CF-End frame,reset their network allocation vector and open the wireless medium toDCF contention.

Referring now to FIG. 6, in order to provide quality of service, theaccess point 20 may transmit unicast CF frames addressed to preferredmobile terminals 25. This will cause the mobile terminals that receivethe CF End frames to reset their network allocation vector and startusing distributed coordination function. If only selected mobileterminals receive unicast CF-End frames, while all other mobileterminals still have their network allocation vector set and areprevented from transmitting, the selected mobile terminals will haveprivileged access to the wireless medium.

The beacon is sent periodically at times denoted by the Target BeaconTransmit Time (TBTT). At each TBTT, an access point 20 must wait for thewireless medium to become idle prior to transmitting the beacon 180.Thus, as illustrated in FIG. 6, at the occurrence of TBTT 120, thenetwork allocation vectors are set for all mobile terminals associatedwith a particular access point 20. Absent any further actions, the NAVwill be set for each of the mobile terminals 25 for the entire period oftime indicated at 125. If the access point 20 transmits a unicast CF-Endframe to mobile terminal 1 at 130. Mobile terminal 1 resets its NAV andthen uses the distributed coordination function for time period 135.When access point 20 transmits a unicast CF-End frame to mobile terminal2 at 140, both mobile terminal 1 and mobile terminal 2 use thedistributed coordination function at 145. Prior to transmission of thebroadcast CF-End frame at 150, only mobile terminal 1 and mobileterminal 2 are using the distributed coordination function and hencehave easier access to the wireless medium. All other mobile terminals 25are only able to communicate with the access point 20 when polled. Afterthe broadcast, the end frame is transmitted at 150 and all mobileterminals may begin using the distributed coordination function for timeperiod 155 until a next beacon 160 is received.

Referring now to FIGS. 7-9, a further embodiment of a proxy isillustrated wherein during a contention period, the network allocationvector is used to protect the wireless medium for the duration of aframe exchange sequence. An STA that receives a frame that is notaddressed to the STA is required to update its NAV value using the valuein the duration/ID field 165 as shown in FIG. 7 of the received frame.

An access point 20 may give prioritized access to a given mobileterminal 25 by transmitting a frame to the mobile terminal with a valuein the duration/ID field 165 indicates a time period that is larger thanrequired. Thus, as shown in FIG. 8, when an access point 20 transmits aframe to the first mobile terminal 25 a, the one or more STAs alsoreceiving the frame set their network allocation value in accordancewith the received value. Since the intended recipient mobile terminal 25a of the frame does not update its NAV, and the extended NAV will notaffect the mobile terminal 25 a to which the frame has been addressed.The address mobile terminal 25 a will have priority access for theduration of the NAV

This mobile terminal 25 a will have sole access to the wireless mediumfor as long as the extended NAV lasts, as illustrated in FIG. 9. Thetime T denotes the time during which all other mobile terminals have settheir NAV and mobile terminal 25 a has exclusive access to the wirelessmedium. The regular NAV denotes the NAV that would have been set bystandard usage of the duration field. Extended NAV denotes the NAV asset by the above proposed proxy. The time T in FIG. 9 should be longerthan DIFS+CW*slot_time to guarantee that the DCF mechanism in mobileterminal 25 a can start a transmission during time period T. CW is thecontention window, DIFS is the DCF interframe spacing and slot_time isthe 802.11 SlotTime. This described system would provide an implicitpolling of the mobile terminal 25 a.

In the following embodiments focus upon the QoS proxy implementationswill be made at the protocol layers above the IEEE 802.11 WLAN protocol.

FIG. 10 shows one protocol stack 200 of a mobile terminal and thecorresponding protocol stack 210 at the AP, and a protocol stack of apeer end user 200 located at the wired LAN 220. As it can be seen the AP210 utilizes one type of MAC and physical layer for the wired side 250and the 802.11 MAC and physical layer 260 for the wireless side. It canalso be seen that the IP layer as well as the TCP layer are transparentthrough the AP 210.

In the following embodiment the QoS Proxy modifies the ToS (Type ofService) field in the IP version 4 header, as seen in FIG. 11. Prior totransmitting, or relaying, a received IP datagram the QoS Proxy modifiesthe ToS field. For a preferred user the QoS Proxy will modify the ToSfield to indicate a high QoS class, whilst for a regular user the QoSProxy will modify the ToS field to indicate a low QoS class. The ToSfield is currently used for negotiating bandwidth properties such asdelay and throughput according to DiffServ mechanism, RFC(Informational) no. 2475, which is implemented in many routers. Byadjusting the ToS field the packets from the terminal 200 will besubject to a lower service level towards peer 220. It is also possibleto enhance the service for given terminal 200 by adjusting the ToS fieldcorrespondingly. It should be noted that the QoS proxy will recalculatethe checksum of IP datagrams in order to reflect the manipulated ToSfield and still allow checksum operations to be carried out.

Similar to the implementation above, where IP version 6 is used, the QoSProxy modifies the Traffic Class field in the IP version 6 header, seeFIG. 12. For a preferred user the QoS Proxy will modify the TrafficClass field to indicate a high QoS class, whilst for a regular user theQoS Proxy will modify the Traffic Class field to indicate a low QoSclass.

In another embodiment the QoS Proxy will deliberately delay IP datagramor drop IP datagrain for regular users, i.e. users of a low QoSallocation. The deliberate delaying of IP datagrains will have theeffect that the pace by which the higher layers of the sending end whichdelivers IP datagrams to the IP protocol, e.g. TCP, will decrease thetransmitting pace. The increasing round trip time for regular, i.e. lowQoS, users will result in a shorter round trip time for preferred users,i.e. high QoS users.

The effect of dropping IP datagrams may result in a retransmission fromthe higher layer of the sending end user and in a decreased pace bywhich the higher layer of the sending end user delivers IP datagrams tothe IP protocol. This will also cause benefits for the preferred users.

By combining the mechanisms of modifying the ToS field, Traffic Classfield, deliberately delaying IP datagram and deliberately dropping IPdatagrams, a powerful toolbox is given to the QoS Proxy. The behavior ofthe QoS Proxy may be determined by the higher layer protocol above theIP layer. E.g. regular users using TCP may be given precedence overregular users using RTP, or UDP, or any combination thereof.

It can also be noted that the behavior of the QoS Proxy may bedetermined according to the lower layer statistics. For instance theIEEE 802.11 Busy/Idle threshold may determine the delay of IP datagramsuch that if the Busy/Idle threshold is high more IP datagram aredelayed compared to when the Busy/Idle threshold is lower.

In another embodiment the QoS Proxy will split the TCP connection thatspans from the wireless mobile terminal via the AP to e.g. a peer entityin the wired LAN into 2 TCP connections. The split will occur in the QoSProxy and result in 2 TCP connections. The QoS Proxy will then relay TCPsegment floating back and forth from the wireless mobile terminal, andas seen from both end users act as any other peer TCP sender orreceiver.

Similar to the case where the QoS Proxy modifies the ToS field in the IPversion 4 header, the QoS Proxy can modify the window field in the TCPheader, see FIG. 13.

The window field determines an upper limit to the amount of outstandingdata for the sender and consequently an upper limit to its' packettransmission rate.

By increasing the window field for preferred users and/or decreasing thewindow field for regular users, the preferred users may perceive ahigher throughput of the TCP layer and thus an increased QoS.

It can be noted that apart from actually changing the window field whenrelaying a TCP segment, the QoS Proxy could also influence thecommunicating end users to change the window field. This could forexample be done by explicitly controlling links towards the end users.

It is believed that the operation and construction of the presentinvention will be apparent from the foregoing description and, while theinvention shown and described herein has been characterized asparticular embodiments, changes and modifications may be made thereinwithout departing from the invention as defined in the following claims.

1. A method for providing quality of service in a wireless local areanetwork, comprising the steps of: processing received data from at leastone mobile terminal using a quality of service proxy; and providing aquality of service operation to the at least one mobile terminal.
 2. Themethod of claim 1, wherein the step of processing further comprises thesteps of: receiving a frame via the quality of service proxy from amobile terminal; discarding the received frame; and preventingtransmission of an acknowledgment of receipt of the frame back to themobile terminal.
 3. The method of claim 1, wherein the step ofprocessing further comprises the steps of: receiving a frame via thequality of service proxy from a mobile terminal; and discarding thereceived frame.
 4. The method of claim 1, wherein the step of processingfurther comprises the steps of: receiving a frame via the quality ofservice proxy from a mobile terminal; preventing transmission of anacknowledgment of receipt of the frame back to the mobile terminal; andforwarding the frame to a wired network.
 5. The method of claim 1,wherein the step of processing further comprises the steps of: setting anetwork allocation vector for each mobile terminal of a plurality ofmobile terminals associated with an access point; transmitting a unicastCF-End frame to at least one mobile terminal of the plurality of mobileterminals; and resetting a network allocation vector for the at leastone mobile terminal responsive to the unicast CF-End frame to enable DCFaccess to the wireless network.
 6. The method of claim 5, furthercomprising the steps of: broadcasting a CF-End frame to the plurality ofmobile terminals; and resetting the network allocation vector for anyremaining mobile terminals.
 7. The method of claim 1, wherein the stepof processing further comprises the steps of: transmitting a frame froman access point that can be received by each of a plurality of mobileterminals, said frame addressed to a particular mobile station andincluding a value in a duration field that is larger than required;setting a NAV addressed for each mobile terminal to which the frame wasnot addressed according to the indicated value; providing priorityaccess to the access point by the particular mobile station for a timeperiod responsive to the larger than required value.
 8. The methodaccording to claim 1 wherein the wireless local area network is an802.11 network.
 9. The method according to claim 11 wherein the proxymodifies the ToS field in the IPv4 header.
 10. The method according toclaim 1, wherein the proxy modifies the Traffic Class field in the IPv6.11. The method according to claim 1, wherein the proxy deliberatelydelays one or more IP packets.
 12. The method according to claim 1,wherein the proxy deliberately drops one or more IP packets. 13-19.(Cancelled)